Technical Field
The present invention relates to a measurement device that measures voltage and power consumption of a facility in non-contact with a power line and a mounting unit that mounts the measurement device on an external distribution board.
Related Art
It is required to correctly measure the power consumption of each facility from the viewpoint of energy saving. It is necessary to measure the voltage in order to measure the power. When direct wire connection to the power line is performed to measure the voltage, electric work is required, and it is necessary to stop the facility. In order to avoid this trouble, there is a method in which the voltage is measured in a non-contact manner using capacitance coupling by firmly placing an electrode on wiring coating of the power line. When the sensor is placed by the method without requiring electric work, a GND terminal of a sensor circuit cannot be connected to ground (GND).
As to a power measurement method, for example, Patent Document 1 discloses a non-contact voltage measurement method in which a potential difference between a shield and probe is set to zero using an operational amplifier to exclude an influence of a floating capacitance. In a non-contact voltage measurement device disclosed in Patent Document 2, a phase difference of a voltage signal measured by a non-contact voltage measurement electrode is measured to obtain and correct a phase of a voltage signal of an insulated wire, thereby improving measurement accuracy. Patent Document 3 discloses a voltage measurement device that calculates a difference value between a detection signal and a reference potential to control a gain of a feedback loop using a variable capacitance circuit.
In all the methods disclosed in Patent Documents 1 to 3, capacitance coupling is generated between an external noise source and a signal ground line of the measurement circuit, or an electrostatic capacitance (floating capacitance) fluctuates between the signal ground line and the ground, which may result in varying of the sensor output and may negatively affect the measurement accuracy.
Patent Document 1: Japanese Patent No. 3761470
Patent Document 2: Japanese Patent No. 4251961
Patent Document 3: Japanese Patent No. 4629625